The Gow Lake impact structure, northern Saskatchewan

1977 ◽  
Vol 14 (8) ◽  
pp. 1788-1795 ◽  
Author(s):  
M. D. Thomas ◽  
M. J. S. Innes
Keyword(s):  
Impact Crater ◽  
Fine Grained ◽  
Model Studies ◽  
Deformation Structures ◽  
Basement Rocks ◽  
Clear Glass ◽  
Microscopic Features ◽  
Minimum Age ◽  
Central Island ◽  
Quartz Grains

Gow Lake, in the Precambrian Shield of Saskatchewan, is circular, 4 km in diameter, and has a large central island. Granites and quartzofeldspathic gneisses are exposed around the perimeter of the lake, whereas the island is formed largely of brecciated equivalents. Most of the breccias are composed entirely of clastic material, but at one locality fine-grained felted matrices form a significant component of the breccias, and coronas of clear glass surround quartz grains. The latter breccias also contain microscopic features characteristic of shock metamorphism, among which multiple sets of planar deformation structures in quartz are particularly diagnostic. Similar shock metamorphic features have been widely reported from terrestrial meteorite craters; accordingly, Gow Lake is interpreted as a deeply eroded impact crater and the felted matrices as impact melts.A local negative gravity anomaly with an amplitude of 3 mGal centered on the lake is attributed mainly to highly fractured basement rocks underlying the lake, which model studies indicate may extend to a depth of 900 m. A provisional minimum age of 100 Ma is proposed for the crater.

scholarly journals Denudation systematics inferred from in situ cosmogenic <sup>10</sup>Be concentrations in fine (50–100 µm) and medium (100–250 µm) sediments of the Var River basin, southern French Alps

2019 ◽  
Vol 7 (4) ◽  
pp. 1059-1074 ◽  
Author(s):  
Apolline Mariotti ◽  
Pierre-Henri Blard ◽  
Julien Charreau ◽  
Carole Petit ◽  
Stéphane Molliex ◽  
...  
Keyword(s):  
Glacial Cycles ◽  
Size Fractions ◽  
French Alps ◽  
Fine Grained ◽  
Denudation Rates ◽  
Variable Morphology ◽  
Cosmogenic 10Be ◽  
The Impact ◽  
Quartz Grains

Abstract. Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic 10Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (<250 µm) than typically analyzed in 10Be studies, and few studies have measured 10Be concentrations in quartz grains smaller than 100 µm or assessed the impacts of mixing, grain size, and interannual variability on the 10Be concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic 10Be concentrations of quartz grains in the 50–100 and 100–250 µm size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from 10Be analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate, and geology, and we test the impact of these parameters on the observed 10Be concentrations. Both analyzed size fractions returned similar 10Be concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02±0.78)×104 to (4.40±0.64)×104 atoms g−1 of quartz. By comparing expected and observed 10Be concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations 1 year later, and despite variable climatic parameters during that period, interannual 10Be concentrations were in agreement within uncertainties, except for one upper subbasin. The 10Be-derived denudation rates of Var subbasins range from 0.10±0.01 to 0.57±0.09 mm yr−1, and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24±0.04 mm yr−1, in agreement with other methods. Our results demonstrate that fine-grained sediments (50–250 µm) may return accurate denudation rates and are thus potentially suitable targets for future 10Be applications, such as studies of paleo-denudation rates using offshore sediments.

Geochronology of the Belt Series, Montana

1968 ◽  
Vol 5 (3) ◽  
pp. 737-747 ◽  
Author(s):  
J. D. Obradovich ◽  
Z. E. Peterman
Keyword(s):  
Average Rate ◽  
Sedimentary Rocks ◽  
Time Interval ◽  
Depositional History ◽  
Middle Cambrian ◽  
Basement Rocks ◽  
Field Evidence ◽  
Minimum Age ◽  
History Of ◽  
Central Montana

This paper presents new radiometric data that permit some qualified statements to be made on the depositional history of the Belt sedimentary rocks. The period of deposition of sedimentary rocks of the Precambrian Belt Series has been placed within a broad time interval, for they rest on metamorphosed basement rock dated at ~ 1800 m.y. and are overlain by the Middle Cambrian Flathead Quartzite (circa 530 m.y.). Prior geochronometric data gathered during the last decade indicate most of the Belt Series to be older than ~ 1100 m.y.K–Ar and Rb–Sr techniques have been applied recently to a variety of samples selected from the whole gamut of the Belt Series. Glauconite from various formations in the sequence McNamara Formation down to the uppermost beds of the Empire Formation in the Sun River area has been dated at 1080 ± 27 m.y. by the K–Ar method and at 1095 ± 22 m.y. by the Rb–Sr mineral isochron method. A Rb–Sr whole-rock isochron based on argillaceous sedimentary rocks from this 5000-ft section gives an age of 1100 ± 53 m.y. The concordance of the preceding results and the K–Ar ages (1075 to 1110 m.y.) on Purcell sills and lava imply that this age represents the time of sedimentation of these units.A Rb–Sr isochron based on whole-rock samples stratigraphically far below the Umpire Formation— the Greyson Shale, Newland Limestone, Chamberlain Shale, and Neihart Quartzite in the Big Belt and Little Beit Mountains—yields an age of 1325 ± 15 m.y. This result is interpreted as indicating a substantial unconformity beneath the Belt Series, at least in central Montana; it also suggests a major hiatus, unsuspected from field evidence, between the uppermost part of the Empire Formation and the Greyson Shale.The results for the youngest of Belt rocks—the Pilcher Quartzite and the Garnet Range Formation, which are exposed in the Alberton region—are equivocal in that there is widespread dispersion. A large component of detrital muscovite in some of the samples could readily account for the magnitude and sense of this dispersion. A maximum age of ~930 m.y. based on an isochron of minimum slope through the various points may be inferred for this sequence. A K–Ar age of 760 m.y. obtained on biotite from a sill in the Garnet Range Formation provides a minimum age for these younger Belt rocks.Three distinct periods of sedimentation for Belt rocks sampled are suggested at ≥ 1300, 1100, and ≤ 900 m.y., with two substantial hiatuses of 200 m.y. or more. In addition the data for the sequence in the Big and Little Belt Mountains suggest that sedimentation may not have commenced for a period of possibly 400 m.y. after the metamorphism that affected basement rocks, while the data for the Garnet Range and Pilcher sequence suggest that sedimentation ceased some 200 to 400 m.y. prior to the deposition of the Middle Cambrian Flathead Quartzite.To suggest that the Belt sediments were deposited continuously over a period of 400 m.y. or more would imply an unusually low average rate of deposition of ≤ 0.1 ft/1000 yr, and this for the thickest part of the Belt Series. As a realistic expression of the depositional history of the Belt Series, both viewpoints are open to question, but the viewpoint that the Belt basin has been characterized by discontinuous sedimentation would be more in keeping with the principle of uniformity.

Testing direct dating of Alpine faults by luminescence and ESR

2020 ◽  
Author(s):  
Sumiko Tsukamoto ◽  
David Tanner ◽  
Christian Brandes ◽  
Christoph von Hagke
Keyword(s):  
Esr Spectra ◽  
Fault Gouge ◽  
Esr Dating ◽  
Fine Grained ◽  
Infrared Stimulated Luminescence ◽  
Minimum Age ◽  
History Of ◽  
Recent Earthquakes ◽  
Age Range ◽  
Saturation Dose

&lt;p&gt;For a better understanding of the recent exhumation history of the Alps and the distribution of palaeo- and recent earthquakes within the orogen, it is important to elucidate the Quaternary activity of major faults. In this study, we test the applicability of luminescence and electron spin resonance (ESR) dating, which have ultralow closure temperatures, to directly date fault gouge of the Simplon Fault. A dark grey to black, fine-grained fault gouge was sampled near Visp, Switzerland, from an outcrop that exposes rocks that formed at ductile/brittle conditions. Quartz and feldspar grains were extracted from the sample; quartz grains were used for ESR dating, whereas feldspar grains were used for infrared stimulated luminescence (IRSL) dating.&lt;/p&gt;&lt;p&gt;The IRSL measurements reveal that the natural post-IR IRSL signal, stimulated at 225&amp;#176;C (pIRIR&lt;sub&gt;225&lt;/sub&gt;) was in saturation. The pIRIR&lt;sub&gt;225&lt;/sub&gt; signal had an extremely low saturation dose, with a characteristic saturation dose (D&lt;sub&gt;0&lt;/sub&gt;) of ~90 Gy. The natural IRSL signal at 50&amp;#176;C (IR&lt;sub&gt;50&lt;/sub&gt;) is about 80 % of the laboratory saturation, so that this signal is presumably in the field saturation. The IR&lt;sub&gt;50 &lt;/sub&gt;also showed a small D&lt;sub&gt;0&lt;/sub&gt; of ~250 Gy. Although these D&lt;sub&gt;0&lt;/sub&gt; values are unexpectedly small, the IRSL signals can be used to calculate the minimum age of the last seismic movement of the fault.&lt;/p&gt;&lt;p&gt;Both natural and laboratory-irradiated ESR spectra did not contain detectable Ti centre. Therefore, only the Al centre was used for ESR dating. The natural Al centre from the fault was not in saturation, with a preliminary equivalent dose value of ~1500 Gy. Since the last seismogenic movement most likely only partially reset the Al centre, the ESR age can be regarded as the maximum age of the last event.&amp;#160; We show that by combining luminescence and ESR dating, it is possible to narrow down the age range of the last seismic activity on the fault.&lt;/p&gt;

scholarly journals Raman spectroscopy of shocked gypsum from a meteorite impact crater

2016 ◽  
Vol 16 (3) ◽  
pp. 286-292 ◽  
Author(s):  
Connor Brolly ◽  
John Parnell ◽  
Stephen Bowden
Keyword(s):  
Raman Spectroscopy ◽  
Impact Crater ◽  
Hydrothermal Systems ◽  
Microbial Colonization ◽  
Meteorite Impact ◽  
Gale Crater ◽  
Significant Statistical Difference ◽  
Basement Rocks ◽  
Hydrothermal Springs ◽  
Post Impact

AbstractImpact craters and associated hydrothermal systems are regarded as sites within which life could originate on Earth, and on Mars. The Haughton impact crater, one of the most well preserved craters on Earth, is abundant in Ca-sulphates. Selenite, a transparent form of gypsum, has been colonized by viable cyanobacteria. Basement rocks, which have been shocked, are more abundant in endolithic organisms, when compared with un-shocked basement. We infer that selenitic and shocked gypsum are more suitable for microbial colonization and have enhanced habitability. This is analogous to many Martian craters, such as Gale Crater, which has sulphate deposits in a central layered mound, thought to be formed by post-impact hydrothermal springs. In preparation for the 2020 ExoMars mission, experiments were conducted to determine whether Raman spectroscopy can distinguish between gypsum with different degrees of habitability. Ca-sulphates were analysed using Raman spectroscopy and results show no significant statistical difference between gypsum that has experienced shock by meteorite impact and gypsum, which has been dissolved and re-precipitated as an evaporitic crust. Raman spectroscopy is able to distinguish between selenite and unaltered gypsum. This shows that Raman spectroscopy can identify more habitable forms of gypsum, and demonstrates the current capabilities of Raman spectroscopy for the interpretation of gypsum habitability.

scholarly journals Exceptionally preserved conodont apparatuses with giant elements from the Middle Ordovician Winneshiek Konservat-Lagerstätte, Iowa, USA

2017 ◽  
Vol 91 (3) ◽  
pp. 493-511 ◽  
Author(s):  
Huaibao P. Liu ◽  
Stig M. Bergström ◽  
Brian J. Witzke ◽  
Derek E. G. Briggs ◽  
Robert M. McKay ◽  
...  
Keyword(s):  
New Genus ◽  
Impact Crater ◽  
Soft Part ◽  
Basal Bodies ◽  
Upper Ordovician ◽  
Middle Ordovician ◽  
Fine Grained ◽  
New Family ◽  
Clastic Sediments ◽  
The Common

AbstractConsiderable numbers of exceptionally preserved conodont apparatuses with hyaline elements are present in the middle-upper Darriwilian (Middle Ordovician, Whiterockian) Winneshiek Konservat-Lagerstätte in northeastern Iowa. These fossils, which are associated with a restricted biota including other conodonts, occur in fine-grained clastic sediments deposited in a meteorite impact crater. Among these conodont apparatuses, the common ones are identified asArcheognathus primusCullison, 1938 andIowagnathus grandisnew genus new species. The 6-element apparatus ofA.primuscomprises two pairs of archeognathiform (P) and one pair of coleodiform (S) elements. The 15-element apparatus ofI.grandisn. gen. n. sp. is somewhat reminiscent of the prioniodinid type and contains ramiform elements of alate (one element) and digyrate, bipennate, or tertiopedate types (7 pairs). Both conodont taxa are characterized by giant elements and the preservation of both crowns and basal bodies, the latter not previously reported in Ordovician conodont apparatuses. Comparison of the apparatus size in the Winneshiek specimens with that of the Scottish Carboniferous soft-part-preserved conodont animals suggests that the Iowa animals were significantly larger than the latter. The apparatus ofA.primusdiffers conspicuously from the apparatuses of the prioniodontidPromissumfrom the Upper Ordovician Soom Shale of South Africa although the apparatus architecture ofI.grandisn. gen. n. sp. shows some similarity to it. Based on the Winneshiek collections, a new family Iowagnathidae in Conodonta is proposed.

scholarly journals High-performance process fluids used for vibration finishing of parts with granular media made of natural material “Baykalit”

2021 ◽  
Vol 2131 (4) ◽  
pp. 042028
Author(s):  
V Lebedev ◽  
V Shumyacher ◽  
Ye Kolganova ◽  
D Krivosheev
Keyword(s):  
High Performance ◽  
Granular Media ◽  
Cutting Tool ◽  
High Hardness ◽  
Natural Material ◽  
Initial Surface ◽  
Fine Grained ◽  
Siliceous Rock ◽  
Process Fluid ◽  
Quartz Grains

Abstract The results of studies of the technological capabilities of granular media made of natural material “Baykalit” in the conditions of vibration technological systems are presented. Baikalit is a siliceous rock-fine-grained quartzite (microquartzite) - with an aggregate structure of quartz grains measuring 1.5-3 microns with sharp boundaries between these very grains. The granules obtained as a result of crushing the mineral rock Baikalit have a sufficiently high hardness (at least 6.0 - 7.0 on the Mohs scale). The presence of many wedge-shaped vertices along the perimeter of the granules and the arbitrariness of the shape allows us to consider them as a universal cutting tool that has access to various surfaces of complexity. It is shown that vibration treatment with granular media made of natural material “Baykalit” reduces the height of the initial surface micrprofile by 0.2-0.3 microns and is an effective way to remove burrs when processing parts with a surface microprofile height of more than 0.63 microns. The use of process fluids, which include increasing the wetting capacity of both Baikalit and processed workpieces, reduces the technological time of vibration processing by 1.5 times. The presence of components in the process fluid, such as protective colloids (Na CMC), prevents the sludge from sticking to the galtovochnye bodies, that is, prevents the “salting” of their profile, reduces the rigidity of the layer on the surface of the galtovochnyh bodies and workpieces, which contributes to productivity growth.

scholarly journals The use of spectral natural gamma-ray analysis in reservoir evaluation of siliciclastic sediments: a case study from the Middle Jurassic of the Harald Field, Danish Central Graben

2003 ◽  
Vol 1 ◽  
pp. 349-366 ◽  
Author(s):  
Ida L. Fabricius ◽  
Louise Dahlerup Fazladic ◽  
Armgard Steinholm ◽  
Uffe Korsbech
Keyword(s):  
Middle Jurassic ◽  
Gamma Ray ◽  
Clay Content ◽  
Heavy Minerals ◽  
Reservoir Evaluation ◽  
Fine Grained ◽  
Natural Gamma ◽  
The Difference ◽  
Siliciclastic Sediments ◽  
Quartz Grains

Danish Central GrabenA cored sandstone interval from the Middle Jurassic Harald Field of the Danish North Sea was chosen for an investigation of the mineralogical sources for the gamma-ray activity, and with the purpose of determining how the Spectral Natural Gamma (SNG) log could be used as an indicator of reservoir quality. Core intervals of quartz arenites and quartz wackes were selected. Although no linear relationship was found between clay content and potassium (K), thorium (Th), or uranium (U), the K content characterises three discrete lithofacies. Lithofacies I has a grain-supported texture, with a predominance of quartz grains; only minor fine-grained matrix is present. Sandstones of lithofacies I have a low K content and most of the K is hosted in feldspar. Porosity varies between 23% and 28% and permeability is in the range 200–2000 mD. Lithofacies II sandstones have a grain-supported texture, with a predominance of quartz grains; fine-grained matrix fills the intergranular volume. Sandstones of lithofacies II have an intermediate K content, with K-feldspar, mica, and illite as the main sources. Porosity varies between 11% and 17% and permeability is in the range 0.4–25 mD. Lithofacies III has a matrix-supported texture with quartz grains floating in a clay-rich matrix. Samples from lithofacies III have the highest K signal. Illite and illitised kaolinite are roughly equal in importance as sources of K. Porosity is up to 11% and permeability up to 0.5 mD. The Th and U content of all lithofacies is governed primarily by the presence of heavy minerals; no apparent general relationship between U and Total Organic Carbon (TOC) was found. Comparisons between the core measurements of K, Th, and U, and the SNG log disclosed a discrepancy between the calibrations of laboratory and borehole measurements. For U the discrepancy contains an erratic element, whereas the difference for K and Th can be eliminated by correction factors. Thus, the conclusions based on laboratory measurements appear to be applicable to the log data, and, using corrected K values, the facies subdivision can be extended throughout the reservoir section based on the SNG log.

scholarly journals Soft sediment deformation in dry pyroclastic deposits at Ubehebe Crater, Death Valley, California

Geology ◽  
2020 ◽  
Author(s):  
Greg A. Valentine ◽  
Judy Fierstein ◽  
James D.L. White
Keyword(s):  
Wet Deposition ◽  
Death Valley ◽  
Soft Sediment ◽  
Pyroclastic Deposits ◽  
Fine Grained ◽  
Deformation Structures ◽  
Pyroclastic Surges ◽  
Sediment Deformation ◽  
Soft Sediment Deformation ◽  
Steep Slopes

Soft sediment deformation structures are common in fine-grained pyroclastic deposits and are often taken, along with other characteristics, to indicate that deposits were emplaced in a wet and cohesive state. At Ubehebe Crater (Death Valley, California, USA), deposits were emplaced by multiple explosions, both directly from pyroclastic surges and by rapid remobilization of fresh, fine-ash-rich deposits off steep slopes as local granular flows. With the exception of the soft sediment deformation structures themselves, there is no evidence of wet deposition. We conclude that deformation was a result of destabilization of fresh, fine-grained deposits with elevated pore-gas pressure and dry cohesive forces. Soft sediment deformation alone is not sufficient to determine whether parent pyroclastic surges contained liquid water and caused wet deposition of strata.

Tracing gold nuggets back to the source: a microchemical analysis of tertiary gold placers in Central Spain.

2021 ◽  
Author(s):  
Santos Barrios ◽  
Juan Gómez Barreiro ◽  
Rafael Pablo Lozano Fernández ◽  
Raúl Merinero Palomares ◽  
Mercedes Suárez Barrios ◽  
...  
Keyword(s):  
Primary Sources ◽  
Lower Paleozoic ◽  
Gold Particles ◽  
Fine Grained ◽  
In Situ Modification ◽  
Basement Rocks ◽  
El Alto ◽  
Alkaline Conditions ◽  
Fe Oxyhydroxides ◽  
Primary Gold

&lt;p&gt;Gold placers are abundant and intensively surveyed in western Iberia since antiquity. Three Cenozoic gold placers covering Neoproterozoic-Lower Paleozoic basement rocks have recently been revealed, which stand out for the number and size of the samples recovered: Salvatierra de Tormes (ST), Santib&amp;#225;&amp;#241;ez el Alto (SA) and Casas de Don Pedro-Talarrubias (CSDP). To date, primary sources remain undiscovered. We have combined microchemical, inclusion analysis and morphology of gold nuggets to define the placer gold signature and its relationship with bedrock primary sources and infer mineralization styles. Coarse gold particles prevent secondary resetting of source signature and increase the chances to investigate mineral assemblages. Nuggets morphology analysis have reveled that ST and SA deposit are fluvial &quot;trunk&quot; placers, while CSDP represents an autochthon or colluvial placer type. Four different types of gold have been defined in nuggets: core gold (T1), rim gold (T2) fine grained gold in Fe-oxyhydroxides aggregates (T3) and &quot;mustard&quot; gold (Au+Sb-Pb-Fe-oxides) (T4).&lt;/p&gt;&lt;p&gt;Based on those categories we have explored primary and secondary signatures in the deposits. Lode signature is observed in the core of nuggets (T1) with a fineness between 800 and 1000. Alloy composition ranges from binary (Au:Ag) in SA to ternary (Au:Ag:Cu) in ST and CSDP. Sulphides and sulfarsenides dominates inclusions association in ST, while Sb- and Sb-Pb-Fe phases appear in ST and CSDP respectively. CSDP primary gold shows a distinct Hg content. The identification of mineral phases non-compatible with supergene conditions in gold and textural remnants of annealing microstructures, point to an hypogenic origin of T1 in all deposits and coul be compatible with a mesothermal system (&lt;400&amp;#186;C) in which, CSDP represents the higher T and SA the lower T end. A hybrid hydrothermal-magmatic system is proposed.&lt;/p&gt;&lt;p&gt;Secondary signature is complex and reveals several stages. Older evidence of in-situ modification of primary gold was found in CSDP gold-bearing quart fragments, with pervasive alteration under oxidizing and alkaline conditions. This process liberated gold from T1 and primary phases (e.g., aurostibite), leading to the formation of auroatimonades and &quot;mustard&quot; gold (T4), showing a complex textural pattern. Gold particles were subsequently modified during fluvial transport and deposition through the interaction with fluids, which activated Ag-leaching processes, resulting in the development of gold-rich rims (T2). Partial dissolution and re-precipitation of gold in reduction conditions formed very fineness gold particles embedded in Fe oxy-hydroxides (T3).&lt;/p&gt;

scholarly journals Petrographic Investigation of Target Rock Transformation under High Shock Pressures from the Colônia Impact Crater, Brazil

2017 ◽  
Vol 7 (1) ◽  
pp. 13 ◽  
Author(s):  
Victor F. Velázquez ◽  
Rodrigo F. Lucena ◽  
Jose M. Azevedo Sobrinho ◽  
Alethéa E. Martins Sallun ◽  
William Sallun Filho
Keyword(s):  
Shock Waves ◽  
Impact Crater ◽  
Small Scale ◽  
Impact Melt ◽  
Basement Rocks ◽  
High Shock ◽  
Target Rock ◽  
Deformation Phase ◽  
Deformation Features ◽  
The Impact

The Colônia impact crater, developed on crystalline basement rocks, offers an excellent example of one of the most unique features of the impact process: the effects of shock waves on textural and mineralogical changes of the target rock. The impact melt-bearing impactites were derived essentially from the igneous and metamorphic rocks, including granite, mica schist, granitic gneiss, and quartzite. Investigations using optical microscopy indicate that the effect of shock waves on those lithologies caused a wide variety of deformation features and generation of new materials. The most common features include fluidal textures, unusual rearrangement patterns between grains, recrystallization, decomposition and precipitation of new phases, agglutination of glassy and crystalline spherules, and the mobilized melt formed different types of impact melt particles. These transformations cover processes that may involve a new grain growing at the expense of parental grains of the same species, or crystallization of different mineral types from component-providing grains until a complete textural and compositional change of the target rocks occurs. Small-scale structures in deformed rocks are particularly interesting for exploring elastic-plastic deformation, phase transformations, and generation of impact melt products.

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